Method and apparatus for casting

ABSTRACT

A method and apparatus for producing a cast product. The apparatus includes a mould ( 10 ) having a mould cavity ( 12 ) and a runner ( 14 ) which communicates with the mould cavity ( 12 ), The mould ( 10 ) is connected to a feed pipe ( 11 ) for feeding molten material to the mould cavity ( 12 ) through the runner ( 14 ). The mould ( 10 ) includes a valve ( 20 ) for closing the runner ( 14 ) to material flow upon receipt within the mould cavity ( 12 ) of sufficient molten material. The method includes closing the runner ( 14 ) by the valve ( 20 ) upon receipt of sufficient molten material within the cavity ( 12 ) and thereafter disconnecting the feed pipe ( 11 ) from the mould ( 10 ) and inverting mould ( 10 ). The method further includes relatively displacing the mould ( 10 ) and the feed pipe ( 11 ) for connection of the feed pipe ( 11 ) to a further mould and allowing the molten material to solidify within the mould cavity ( 12 ) prior to removal therefrom.

The present invention relates to a method of casting and to castingapparatus for performing the method. The casting method has beendeveloped principally for the casting of aluminium disc brake calipersand it will therefore be convenient to describe the method and apparatusof the invention as it applies to that application. However, it shouldbe appreciated that the invention is not limited to that particularapplication and could be employed, for example, for other cast aluminiumproducts, or for cast products of different metals, such as brass ormagnesium.

The casting method of the invention is of the type in which the moltencasting material is fed upwardly or in a counter-gravity direction.Counter gravity casting is disclosed in several patent specifications,including U.S. Pat. No. 4,733,714, U.S. Pat. No. 4,862,945 and U.S. Pat.No. 5,730,203. A particular benefit of such casting is that theinjection pressure applied to the molten metal can be balanced againstthe downward gravity pressure so that the mould cavity can be filled ina non-turbulent manner, thereby minimising the formation of oxidesthrough the cast product, which otherwise affect the strength of thecasting formed. The minimisation or virtual complete elimination ofoxides in the cast product is extremely advantageous in the productionof disc brake calipers, because of the high loading such calipers aresubject to in use.

One problem which has arisen with counter-gravity casting is that thefeed pressure of the molten metal must be maintained while the metalsolidifies, or the molten metal will flow back under gravity from themould cavity, through the feed pipe to the supply of molten metal, whenthe feed pressure is released. While maintaining the feed pressure isnot difficult, the necessity to do this severely limits castingproductivity or cycle time.

As discussed in U.S. Pat. No. 4,733,714, counter-gravity casting canemploy rotation or inversion of the mould after the molten metal hasbeen pumped or injected into the mould cavity. This advantageouslypermits disconnection of the feed pipe from the mould, so that the pipecan be connected to a new mould to feed molten metal thereinto, whilethe molten metal in the mould from which the pipe has been disconnected,solidifies. This method accelerates the rate of production compared toother methods of counter-gravity casting in which the feed pipe remainsconnected to the mould until such time as the molten metal hassolidified sufficiently for disconnection.

The above method employs a feed reservoir internally of the mouldcavity, which is located below the mould cavity when molten metal isbeing fed into the mould, but which is located above the mould cavitywhen the mould is inverted. The feed reservoir feeds molten metal to themould cavity when the mould is inverted and thereby provides a source ofpressure by way of a metalostatic head.

The method is particularly suited for use with sand moulds, because suchmoulds can be produced continuously and then moved to the molten metalsource for filling and then moved away for cooling. Also, in a sandmould, the runner which communicates with the mould cavity and the feedpipe can be closed simply by forcing the wall of the runner inwards,with a suitable plunger or the like. Therefore, it is a simple matter toclose the runner to prevent reverse or backflow of molten metal to themetal source upon release of feed pressure.

Sand moulds are not however, very suitable for producing cast productsrequiring high tensile strength. This is partly because mould sandsgenerally provide poor rates of heat transfer and consequently slowmetal solidification rates, so that the cast product has a very coarsemicrostructure. For increased strength, a fine microstructure isdesirable. Aluminium disc brake calipers are subject to very highloading and it is therefore extremely desirable that they be producedwith a fine microstructure rather than a coarse microstructure. It ishowever the case that disc brake calipers have been cast previously fromsand moulds, but this has been limited to cast iron calipers. However,the use of cast iron for disc brake calipers these days is undesirable,principally because of the significant weight increase compared toaluminium calipers.

According to the present invention there is provided a method ofproducing a cast product, said method employing a mould having a mouldcavity and a runner which communicates with the mould cavity, said mouldbeing connected to a feed pipe for feeding molten material to said mouldcavity through said runner, said mould including a valve arrangement forclosing said runner to material flow upon receipt within said mouldcavity of sufficient molten material, said method including closing saidrunner by said valve arrangement upon receipt of said sufficient moltenmaterial within said cavity and thereafter disconnecting said feed pipefrom said mould and inverting said mould, and further includingrelatively displacing said mould and said feed pipe for connection ofsaid feed pipe to a further mould and allowing said molten material tosolidify within said mould cavity prior to removal therefrom.

Further, the present invention provides a casting apparatus including amould having a mould cavity, and a runner which communicates with saidmould cavity, a feed pipe for connection to said mould for feedingmolten material to said mould cavity through said runner, a valvearrangement for closing said runner to material flow upon receipt withinsaid mould cavity of sufficient molten material, said apparatus beingoperable to disconnect said feed pipe from said mould following closureof said runner by said valve arrangement and said mould being mountedfor inversion following said disconnection, said apparatus further beingoperable to relatively displace said mould and said feed pipe forconnection of said feed pipe to a further mould of said apparatus.

The casting process and apparatus of the present invention is envisagedto be almost exclusively for use in the casting of metal and while it ispossible that materials other than metals would be employed, hereinafterreference will be made to metals only.

In the method of the invention, the valve arrangement facilitates earlydisconnection of the feed pipe from the mould, to further acceleratethis type of casting from prior art casting methods in which mouldinversion does not take place. Accordingly, feed pipe disconnection canoccur as soon as the valve arrangement has closed the mould runner andif desirable, even before the mould is inverted. The feed pipe can thusbe connected to a further mould without having to wait for the firstmould to rotate to the inverted position.

The above arrangement also simplifies the connection between the mouldand the feed pipe because the connection is not required to permitrelative rotation between the mould and the feed pipe. Thus, theconnection may for example, be a simple abutting connection withengagement between the two components, which connection might otherwisebe inappropriate in circumstances where relative rotation was required.The abutting connection would preferably seal against leakage throughthe connection.

The mould according to the present invention preferably is a permanentmould, in particular rather than a sand mould. In addition to thedrawbacks associated with the use of sand moulds for disc brake caliperproduction discussed earlier herein, sand moulds typically are furtherinappropriate for disc brake caliper casting because sand granules canbe dislodged from the mould during casting and become part of the castproduct, affecting its strength characteristics. Castings produced insand moulds also are typically dimensionally inaccurate and exhibit poorsurface finish.

The mould may include a mould cavity of any suitable form and mayinclude a feed reservoir to feed the cavity with molten metal when thefeed pipe is disconnected and the mould has been inverted. Such a feedreservoir preferably is located above the mould cavity in the invertedcondition of the mould, so as to feed the molten metal under gravity.Pumping or pressure may alternatively be adopted, in particular if thereservoir is located other than above the mould cavity in the invertedcondition of the mould.

In the above arrangement, the runner can communicate directly with thefeed reservoir so that feed of molten metal takes place through therunner and the feed reservoir prior to the mould cavity.

The feed pipe preferably feeds upwardly to the mould, so that when therunner is closed, molten metal within the feed pipe and possibly alsowithin the runner, can flow back through the feed pipe to the moltenmetal source. The feed pipe may feed vertically into the mould, say atthe centre-line of the mould, or at any angle thereto. When casting adisc brake caliper, an angle of attack of about 45° may be appropriate.Alternatively, for other cast products such as wheels or steeringknuckles a vertical attack might be preferred.

The valve arrangement can take any form suitable to close flow of moltenmetal through the runner. A valve for use in the invention preferably isone which provides for automatic closure of the runner when pressurecausing molten metal to flow counter to gravity is released. The valvemay include a ball which floats in the molten metal and which is liftedaway from a valve seat when molten metal is flowing under pressure inthe direction towards the mould cavity, to permit that flow, and whichcloses the runner by cooperating with the valve seat when the pressureis released and the flow stops or reverses. The ball therefore can bemade out of a material that has a relatively lower density than themolten metal. The valve seat may take any suitable form suitable tocooperate with the ball and to thereby block the runner against flow ofmolten metal in a direction away from the mould cavity.

In an alternative form, the valve arrangement includes a valve member inthe form of a ball, which can be shifted by shifting means between anopen position in which molten metal can flow past the ball, and a closedposition in which flow of molten metal is blocked. The ball may be onewhich floats in the molten metal, so that the shifting means is operableto shift the ball only to the closed position from the open position,whereas the ball can shift by floating to the open position incircumstances when there is a flow of molten metal and the shiftingmeans is not maintaining the ball in the closed position. The shiftingmeans may include a rod or plunger which acts on the ball, to promoteits movement between the open and closed positions. The runner mayinclude a valve seat to cooperate with the ball and the valve seat maybe formed by a conical portion of the runner into which the ball canenter and seat.

In one arrangement, the valve ball is biased away from the valve seat sothat an actuating mechanism can be employed when necessary to shift theball to the seated valve closed position. In an alternative arrangement,the ball may be allowed to float in the molten metal being pumped to themould cavity and shifting means, such as described earlier, is arrangedto cause the ball to seat within or against the valve seat. An externalactuator can be provided to actuate the push rod or pin as necessary.

Preferably the ball is made from a sacrificial material which can bediscarded at a suitable point in the casting process. For example, theball may be formed of a material such as fly-ash, the binder of whichcan survive the temperature of aluminium casting (about 750° C.), butwhich will not survive at an elevated temperature, such as 1000° C., atwhich temperature the binder breaks down. The desirability for such amaterial is to simplify the recovery of waste cast product which isformed by molten metal which solidifies outside the mould cavity, suchas within the runner. That waste material is removed from the castproduct during finishing of the product and it is desirable to recyclethat waste for subsequent casting, rather than to just discard it.However, it generally will be the case that the ball will form part ofthe waste cast product and because the ball will be of a differentmaterial to that of the product, the ball has to be removed from thewaste cast product before the rest of that product can be recycled. Asacrificial material can be easily removed by heating the waste castproduct to an elevated temperature to separate the material from theproduct by combustion. Fly-ash is a material that can be removedeffectively by this process. Fly-ash additionally is advantageousbecause it will not deteriorate at the molten temperature of aluminiumand therefore can be effectively used as a material for valveconstruction, but will decompose for removal by elevating thetemperature well above the molten temperature.

Other methods can be used to separate the ball material from the wastecast product. For example, the ball material may be removed by sandblasting whereby the ball is broken down for removal. Alternatively theball may be formed from a non-wetting material that can be separatedeasily from the cast material. Fly-ash can achieve this, as can certainceramic composite materials.

The valve arrangement could employ a valve member of a form other than aball and the invention includes within its scope a valve member of anysuitable shape or construction that can close the runner as required.Other forms of valve member can include a rotational valve member thatpermits flow in one position of rotation and which closes against flowin a different position, or such valve members that are collapsible, orthat chill to solidify the molten metal.

The method according to one embodiment of the invention involves thevalve arrangement actuating to close the runner after the mould cavityand any feed reservoir is filled sufficiently, and thereafterdisconnecting the feed pipe from the mould. Inversion of the mould cantake place immediately, at any time following actuation of the valvearrangement. It may for example take place as soon as the feed pipe isdisconnected from the mould or alternatively the mould may be shiftedaway from the feed pipe, or the feed pipe away from the mould beforeinversion takes place. The timing of the inversion may also be dependenton the type of material being cast and the type of casting being made.

In one preferred arrangement, an array of moulds is provided forsuccessive feeding through a single feed pipe. Preferably the array isformed in a circular manner about a central axis, and the array isrotated incrementally, or is indexed about the axis as each mould isfed. A suitable turntable could be employed for this purpose.Conveniently, the array can include sufficient moulds such that the castproduct of each mould solidifies as the array rotates and can be removedfrom the respective mould, prior to that mould returning forreconnection to the feed pipe. In this arrangement, inversion of themould and indexing of the array can be immediate upon the valvearrangement closing the runner. Cooling of the molten metal in the mouldcan also commence immediately.

Other equally applicable arrangements can be employed, such as an arraywhich is not circular, but which might for example move on a conveyor.Alternatively, the moulds may be generally stationary and the feed pipemay shift between them. Still alternatively, a combination of mould andfeed pipe movement may be employed.

As discussed earlier, the rate of solidification of the cast product isimportant for achieving a desirable microstructure. Permanent steelmoulds offer high heat transfer rates compared to sand moulds and thoserates can be increased by forced heat extraction using air and/or watercooling. The rates can alternatively or additionally be accelerated byinjecting suitable gas into the mould cavity, to fill the evolvingshrinkage gap between the mould cavity wall and the solidifying casting.Shrinkage of the casting occurs during solidification and the castingtends to move away from the mould cavity wall, leaving a gap filled withair. The air gap actually insulates the casting from the mould cavitywalls so that the rate of heat transfer from the casting slows andsolidification takes longer, thereby increasing overall cycle time. Agas such as helium, has a high heat transfer coefficient and thereforeit promotes heat transfer rather than insulating against it.Advantageously, the mould may include a suitable connecting part forconnection of a gas hose thereto and the arrangement can be such as toconnect a hose to the mould at a suitable time during metalsolidification. That may be after mould inversion, but not necessarily.The connection therefore can be made at any suitable time, so thatpermanent connections are not required, thereby simplifying theconstruction of the mould and the casting apparatus.

The reduction in cycle time that can be made by cooling the actualmould, can alternatively, be made by cooling the plate or platen towhich the mould is attached.

The present invention is very flexible in relation to cooling rates,because air and water cooling, and the use of high coefficient coolinggases can be varied as required to cause faster or slowersolidification. Sand moulds typically do not have such flexibility.

The invention provides its principal advantages when the mould employedis a permanent mould, preferably a steel permanent mould. As discussedearlier, the use of a valve arrangement permits the use of permanentmoulds rather than sand moulds and the use of permanent steel moulds,along with gases having high heat transfer coefficients and air and/orwater cooling all contribute to faster casting solidification andtherefore lower cycle times. That faster solidification also permits theproduction of aluminium disc brake calipers, with the necessary finemicro-structure. The valve arrangement therefore plays an important partin the invention, by facilitating the use of permanent moulds with theresultant advantages achieved thereby.

Also, the amount of cooling provided by gases having high heat transfercoefficients, and by air and/or water, can be adjusted by suitablecontrol arrangements, so that in casting machinery that employs aplurality of moulds in a casting cycle, the moulds for a range ofdifferent products can be introduced into that cycle rather than beingrestricted to moulds for a single product. For example, in continuouscasting machinery, in which moulds are presented to a feed pipe on acontinuous basis for charging with molten metal and are then moved awayfor the molten metal to solidify, sand moulds are typically employed,with the moulds being produced in a different machine, or a separatepart of the casting machine, on a continuous basis for supply to thecasting machine. In that arrangement the nature of the sand mouldmachinery means that moulds suitable for a single product only areproduced. Therefore, the sand mould process is suitable realisticallyfor a single type of cast product only in any one production cycle andwhen a different type of product is to be cast, the operating parametersof the casting line must change, to suit the new manufacturing andcasting requirements of the mould, such as the new mould shape and thechange in volume of molten material. However, the present inventionadvantageously can adjust the rates of cooling applied to differentmoulds, so that the cycle time for the moulds for two different productscan be identical. Accordingly, the casting machine can operate on a setcycle for a wide variety of different products by adjusting as necessarythe cooling applied to different moulds to suit the cycle time of themachine. This adjustment is relatively simple and can be a programmedfeature of the casting machinery. Also, it is a relatively simple matterwhen permanent moulds are employed, to introduce a different mould ormoulds into the casting cycle and for the casting machinery to beadjusted to suit the introduced mould or moulds and this ideally can bean automatic adjustment that the casting machinery makes as itrecognises a new mould entering the cycle. Thus, the present inventionprovides flexibility for short production runs, which are not suited tosand mould casting.

For a better understanding of the invention and to show how it may beperformed, a preferred embodiment will now be described, by way ofnon-limiting example only, with reference to the accompanying drawing.

FIG. 1 is a cross-sectional view of an apparatus according to oneembodiment of the invention and shows a mould 10 in engagement with afeed pipe 11. As shown, the feed pipe 11 is inclined upwardly and inpractice would extend to and be immersed in a bath of molten metal.Molten metal is fed through the feed pipe by any one of a variety ofmechanisms, such as by pumping or by pressurising the bath. The feedpipe 11 therefore feeds the mould 10 in a counter-gravitational manner.

The mould 10 includes a mould cavity 12, which in the illustrated formshown in FIG. 1, is shaped to cast a disc brake caliper. The mouldcavity 12 is in communication with a feed reservoir 13, while the feedreservoir 13 is in communication with a runner 14. It is clear from FIG.1, that the mould cavity 12 is positioned above the feed reservoir 13and this is the correct orientation for counter-gravity casting.Accordingly, molten metal is fed upwardly through the feed pipe 11,through the runner 14 and the feed reservoir 13, and into the mouldcavity 12. By this orientation, the advantages of counter-gravitycasting can be obtained.

The feed pipe 11 is shown in abutting connection with a projectingportion 15 of the mould 10 and the nozzle 16 of the feed pipe 11 isaligned with an inlet portion 17 of the runner 14. The nozzle 16sealingly engages the projecting portion 15 to prevent leakage of moltenmetal past the connection. Any suitable sealing arrangement can beemployed for that purpose.

The inlet portion 17 is formed to have a right angle curve. The upperend of the portion 17 is arranged to snugly accommodate the ball 19 of aball valve 20. Thus, the upper end 21 is of a diameter slightly greaterthan the diameter of the ball 19.

The ball 19 is engaged by a pin 22 which is accommodated in a boreformed in the projecting portion 15 and biasing means acts between thepin head 23 and the upper surface 24 of the projecting portion 15 tobias the ball 19 towards or into the upper end 21 of the inlet portion17. The pin engages the surface of the ball 19, rather than beingconnected to the ball, so that the ball 19 can be removed with the castproduct when casting is completed without requiring disconnection fromthe pin. When valve actuation is required, an external actuator isoperable to engage the pin head 23 and to push against the pin head tolower the ball 19 for valve actuation.

The inlet portion 17 is arranged to cooperate with the ball 19 to closethe runner 14 and to achieve this, the inlet portion 17 may include avalve seat formed by a conical portion into which the ball 19 may belowered into or against. Accordingly, while it is not apparent from thecross-sectional view of FIG. 1, the neck area 25 may converge in aconical manner so that the ball 19 seats within the neck area 25 uponits downward movement.

The biasing means may provide only a light bias, sufficient to maintainthe ball 18 away from the valve seat in the absence of a valve actuatingforce being applied to the pin head 23. During feed of the molten metalinto the mould 10, the ball 19 may float within the inlet portion 17,but allowing the passage of molten metal therepast.

The feed pipe 11 is movable forward and back by a pneumatic cylinder 26and that movement facilitates connection and disconnection between thefeed pipe and the mould 10 at the projecting portion 15.

The apparatus of FIG. 1 is operable as follows. The mould 10 is broughtinto a position for connection to the feed pipe 11. The feed pipe 11,through the pneumatic cylinder 26, is moved to connect to the mould 10at the projecting portion 15. Feeding means of whatever kind is providedto supply molten metal through the feed pipe 11 and into the inletportion 17 of the runner 14. As discussed, the ball 19 will either floatin the molten metal or be raised into the upper end 21, depending on thearrangement of the biasing means provided. Molten metal will then flowthrough main portion 18 of the runner 14 into the feed reservoir 13 andthen into the mould cavity 12.

When sufficient flow of molten metal has taken place, the ball valve 20will be actuated to seat the ball 19 in the neck area 25, to close therunner 14. Thereafter, the feeding means terminates feed of moltenmetal, and such material that remains in the feed pipe 11 and the inletportion 17 on the feed pipe side of the ball 19 can flow back undergravity to the bath of molten metal. The pneumatic cylinder 26 withdrawsthe feed pipe 11 to disconnect it from the mould 10 and the mould 10, inany sequence or simultaneously, is shifted away from the feed pipe 10and is rotated to be inverted. As the material in the mould cavitysolidifies, molten metal in the feed reservoir feeds into the mouldcavity.

Upon solidification of the molten metal, the mould 10 may bedisassembled to remove the cast product. That product will also includeany solidified material that remains in the feed reservoir 13 and themain runner portion 18, as well as the ball 19. This is the waste castproduct. When the cast product is finished by other required machiningor processing stages, the waste cast product can be removed and returnedto the molten bath for reuse.

Advantageously, the ball can be made from materials of the kinddiscussed earlier, which are easily removable by suitable procedures.

FIG. 2 shows an alternative arrangement to FIG. 1, but in respect onlyof the valve arrangement. Accordingly, where the same features of FIG. 1are shown in FIG. 2, the same reference numerals, plus 100, areemployed.

In FIG. 2, the runner 114 includes an inlet portion 117 and an outletportion 101 that communicates with the feed reservoir 113. The runner114 has a open seat 102 and a closed seat 103. The open seat 102 is sonamed because the ball 119 can engage the seat 102 when molten metal isfed under pressure into the runner 114 from the feed pipe 111 and inthat position a flow path 104 beneath the ball 119 permits flow ofmolten metal past the ball 119. However, when the pressure is releasedand the flow of molten metal attempts to reverse due to gravity, theball 119 will move with the molten metal in the direction toward thefeed pipe 111 and will quickly engage the closed seat 103, closing flowpath 104. As is clear from FIG. 2, the runner 114 is constricted at theclosed seat 103 to have a smaller diameter than that of the ball 119.

The ball valve 119 necessarily must float in the molten metal to seat inthe manner required. Many suitable ball materials can be employed thatwill provide this characteristic.

The arrangement of FIG. 2 advantageously provides for automatic valveoperation and therefore does not require the actuating arrangement ofthe ball valve of FIG. 1. Also, because the ball movement between theopen and closed seats is not great, valve operation is extremely quickand efficient.

The invention described herein is susceptible to variations,modifications and/or additions other than those specifically describedand it is to be understood that the invention includes all suchvariations, modifications and/or additions which fall within the spiritand scope of the above description.

1. A method of producing a cast product, said method employing a mouldhaving a mould cavity and a runner which communicates with the mouldcavity, said mould being connected to a feed pipe for feeding moltenmaterial to said mould cavity through said runner, said mould includinga valve arrangement for closing said runner to material flow uponreceipt within said mould cavity of sufficient molten material, saidmethod including closing said runner by said valve arrangement uponreceipt of said sufficient molten material within said cavity andthereafter disconnecting said feed pipe from said mould and invertingsaid mould, and further including relatively displacing said mould andsaid feed pipe for connection of said feed pipe to a further mould andallowing said molten material to solidify within said mould cavity priorto removal therefrom.
 2. A method according to claim 1, said mouldincluding a feed reservoir in communication with said mould cavity saidmethod involving feeding molten material to said feed reservoir beforeclosing said runner by said valve arrangement and said molten materialin said feed reservoir feeding said mould cavity upon inversion of saidmould as said molten material in said mould cavity solidifies.
 3. Amethod according to claim 2, wherein said feed reservoir is positionedabove said mould cavity when said mould is inverted.
 4. A methodaccording to claim 3, said molten material of said feed reservoirfeeding said mould cavity under gravity.
 5. A method according to claim2, said molten material of said feed reservoir feeding said mould cavityunder pressure exerted on said molten material.
 6. A method according toclaim 2, said runner communicating with said feed reservoir and saidfeed reservoir communicating with said mould cavity, so that said moltenmaterial is fed to said mould cavity through said feed reservoir fromsaid runner.
 7. A method according to claim 1, said method includingfeeding said molten material upwardly counter to gravity through saidfeed pipe to said mould cavity.
 8. A method according to claim 7, saidmolten material being fed substantially vertically to said mould cavity.9. A method according to claim 7, said molten material being fed at anangle of about 45° to said mould cavity relative to vertical.
 10. Amethod according to claim 7, said valve arrangement being operable forautomatic closure of said runner upon pressure causing said moltenmaterial to flow counter to gravity being released.
 11. A methodaccording to claim 1, said valve arrangement includes a ball whichfloats within the molten material as it flows through said runner underpressure and which cooperates with a valve seat to close said runnerwhen said pressure is released and said flow of molten material stops orreverses, said valve being formed from a sacrificial material which cansurvive at the temperature of the molten material during casting, butwhich decomposes at an elevated temperature, said method includingremoving solidified material from said cast product which has solidifiedoutside of said mould cavity, subjecting said solidified material tosaid elevated temperature to melt said solidified material and todecompose said ball, for recovery of said solidified material forre-use.
 12. A method according to claim 11, said ball being formed offly-ash.
 13. A method according to claim 1, wherein inversion of saidmould occurs following disconnection of said feed pipe from said mouldand before said mould is relatively displaced from said feed pipe.
 14. Amethod according to claim 1, wherein inversion of said mould occursfollowing disconnection of said feed pipe from said mould anddisplacement of said mould relative to said feed pipe.
 15. A methodaccording to claim 1, an array of moulds being arranged in a circularlayout and said method including rotating the array for connection ofeach mould successively with said feed pipe.
 16. A method according toclaim 15, said array being rotated at a speed such that a cast productsolidifies in a mould of said array and is removed from said mould priorto returning to said feed pipe.
 17. A method according to claim 1, anarray of moulds being arranged on a conveyor to convey said moulds toand from said feed pipe.
 18. A method according to claim 1, said feedpipe being arranged for movement relative to an array of stationarymoulds.
 19. A method according to 1, including injecting gas into themould cavity during solidification of the cast product within the mouldcavity, said gas being a gas which has a higher heat transfercoefficient than air.
 20. A method according to claim 19, said gas beinghelium.
 21. A method according to 1, including cooling said mould tohasten solidification of said cast product, by air and/or water cooling.22. A method according to claim 1, said mould being a permanent mould.23. A casting apparatus including a mould having a mould cavity, and arunner which communicates with said mould cavity, a feed pipe forconnection to said mould for feeding molten material to said mouldcavity through said runner, a valve arrangement for closing said runnerto material flow upon receipt within said mould cavity of sufficientmolten material, said apparatus being operable to disconnect said feedpipe from said mould following closure of said runner by said valvearrangement and said mould being mounted for inversion following saiddisconnection, said apparatus further being operable to relativelydisplace said mould and said feed pipe for connection of said feed pipeto a further mould of said apparatus.
 24. An apparatus according toclaim 23, said mould being a permanent mould.
 25. An apparatus accordingto claim 23, wherein said mould includes a feed reservoir incommunication with said mould cavity for feeding molten material to saidmould cavity upon inversion of said mould and while said molten materialin said mould cavity solidifies.
 26. An apparatus according to claim 25,said feed reservoir being positioned above said mould cavity in theinverted condition of said mould.
 27. An apparatus according to claim25, wherein said runner communicates with said feed reservoir.
 28. Anapparatus according to claim 23, said valve arrangement includes a ballwhich is lifted away from a valve seat upon flow of molten metal towardsaid mould cavity and which seats against the valve seat when the flowof molten material to said mould cavity stops or reverses, to close saidrunner.
 29. An apparatus according to claim 28, shifting means beingprovided to shift said ball from an open position displaced from saidvalve seat, to a closed position in engagement with said valve seat. 30.An apparatus according to claim 29, said shifting means including rod orplunger which is mounted to engage said ball and to shift said ball tosaid closed position.
 31. An apparatus according to claim 29, saidshifting means being connected to said ball for movement of said ballbetween said open and closed positions.
 32. An apparatus according toclaim 28, said ball being formed to float in said molten material. 33.An apparatus according to claim 28, said ball being biased away fromsaid valve seat and whereby an actuating mechanism is operable to shiftsaid ball into seated engagement with said valve seat.
 34. An apparatusaccording to claim 28, said ball being formed from a sacrificialmaterial which can survive at the temperature of the molten materialduring casting, but which decomposes at an elevated temperature.
 35. Anapparatus according to claim 34, said ball being formed of fly-ash. 36.An apparatus according to claim 23, said valve arrangement comprises arotational valve member which is mounted to act across the runner and isrotatable between open and closed positions.
 37. An apparatus accordingto claim 23, a plurality of moulds being provided in a circular arrayand said array being rotatable incrementally into a position forconnection between successive moulds of said array and said feed pipe.38. An apparatus according to claim 23, wherein said feed pipe shiftsbetween successive moulds into connection therewith.